I could omit you could omit he could omit we could omit you could omit they could omit
V-ing form
I could be omitting you could be omitting he could be omitting we could be omitting you could be omitting they could be omitting
Perfect
I could have omitted you could have omitted he could have omitted we could have omitted you could have omitted they could have omitted
V-ing perfect
I could have been omitting you could have been omitting he could have been omitting we could have been omitting you could have been omitting they could have been omitting
Negation
Simple form
I couldn't omit you couldn't omit he couldn't omit we couldn't omit you couldn't omit they couldn't omit
V-ing form
I couldn't be omitting you couldn't be omitting he couldn't be omitting we couldn't be omitting you couldn't be omitting they couldn't be omitting
Perfect
I couldn't have omitted you couldn't have omitted he couldn't have omitted we couldn't have omitted you couldn't have omitted they couldn't have omitted
V-ing perfect
I couldn't have been omitting you couldn't have been omitting he couldn't have been omitting we couldn't have been omitting you couldn't have been omitting they couldn't have been omitting
Interrogative form
Simple form
could I omit? could you omit? could he omit? could we omit? could you omit? could they omit?
V-ing form
could I be omitting? could you be omitting? could he be omitting? could we be omitting? could you be omitting? could they be omitting?
Perfect
could I have omitted? could you have omitted? could he have omitted? could we have omitted? could you have omitted? could they have omitted?
V-ing perfect
could I have been omitting? could you have been omitting? could he have been omitting? could we have been omitting? could you have been omitting? could they have been omitting?
Interro-negative form
Simple form
couldn't I omit? couldn't you omit? couldn't he omit? couldn't we omit? couldn't you omit? couldn't they omit?
V-ing form
couldn't I be omitting? couldn't you be omitting? couldn't he be omitting? couldn't we be omitting? couldn't you be omitting? couldn't they be omitting?
Perfect
couldn't I have omitted? couldn't you have omitted? couldn't he have omitted? couldn't we have omitted? couldn't you have omitted? couldn't they have omitted?
V-ing perfect
couldn't I have been omitting? couldn't you have been omitting? couldn't he have been omitting? couldn't we have been omitting? couldn't you have been omitting? couldn't they have been omitting?